%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-7-38 on page II-567 in "Changing format directives".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{63.0pt}
%
  \setlength\parindent{0pt}
%  Use biber program

%StartShownPreambleCommands
\usepackage{biblatex} \addbibresource{tlc.bib}
\DeclareFieldFormat{myfieldformat}{\thefield{entrytype}/\currentfield/#1}
\DeclareFieldFormat[article]{myfieldformat}{[\currentfield/#1]}
%StopShownPreambleCommands

\begin{document}
\citefield{Knuth-CT-a}[myfieldformat]{volume}       \\ % a book
\citefield{Knuth:TB10-1-31}[myfieldformat]{volume}  \\ % an article
\citefield{LGC97}[myfieldformat]{year}              \\
\citefield{LGC97}[myfieldformat]{volume}   % a book without volume info
\end{document}
